Technical Field
The present disclosure relates to insulating trenches and their use to insulate a photodiode of an image sensor.
Description of the Related Art
Conventionally, an image sensor comprises a pixel array, each pixel comprising a photosite such as a photodiode and various read, transfer, reset, and other transistors. Each photodiode comprises a semiconductor region for the photogeneration of charge carrier. When the photodiode is illuminated, photogenerated charges build up in the photogeneration region and are then transferred to a read circuit by a transfer transistor associated with the photodiode.
To avoid any crosstalk between neighboring pixels, an insulating trench, currently called DTI (“Deep Trench Isolation”) in the art, is formed around each photodiode of the image sensor.
The simplest photodiode insulation structure comprises a trench filled with silicon oxide. This structure has disadvantages. Particularly, the current photogenerated by the photodiode is smaller than what it should theoretically be. Further, the photodiode has a high dark current.
It would be desirable to provide a trench structure for insulating a photodiode such that the dark current of the photodiode is as low as possible and that the intensity of the photogenerated current of this photodiode is as high as possible.